The invention relates to a portable power tool, comprising a housing which is intended for manual support of the tool and which is formed with an inner surface, and a motor located in the housing and comprising a stator which is surrounded by the inner surface of the housing.
The main problem to be solved by the invention is dividable into two different yet similar problems, namely heat surplus and heat deficit in the tool housing. Dependent on what type of motor, electric or pneumatic, the temperature of the tool housing is raised or lowered to levels which are uncomfortable for the tool operator if he gets into physical contact with or uses the tool housing as a tool supporting handle.
In the case of a pneumatic motor, the exhaust air leaving the motor has a very low temperature, and since the exhaust air is normally directed to and routed around the outside of the motor cylinder or stator the low temperature of the exhaust air is transferred to the surrounding housing. In order to protect the operator from this cold many tools of this type have been provided with an outer lining of a heat insulating plastic material which in many cases, however, has turned out to be insufficient to obtain a comfortable temperature on the outside of the tool housing.
In the case of an electric motor, there is developed heat in the motor stator during operation, and there is usually provided a cooling fan to direct a cooling air flow around the stator so as to transport heat out of the tool housing. This, sometimes in combination with a heat insulating outer lining on the housing, is not sufficient to prevent the housing temperature from being uncomfortably high.
In U.S. Pat. No. 4,643,263, there is described a heat insulating problem resembling the above described problem, as well as a solution to that problem.
In this prior art reference, there is described a portable pneumatic grinder having an air exhaust passage extending through a tubular handle. The handle is provided with an inner tube of a heat insulating material, like a synthetic resin. This inner tube is arranged with a circumferential air gap relative to the handle tube inside surface to, thereby, improve the heat insulating effect.
Differently from the invention, this known device is related to a problem where the available space is not critical for the arrangement of a heat transfer retarding device. Accordingly, the described plastic type heat insulating tube would be too space demanding for use as a heat screening device in a manually supported motor housing of a power tool.